/*
 * TransactionalIterator.java   ver    16 Nov 2009
 * 
 * Copyright (c) 2009 mentalsmash.org
 * 
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 * http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 *
 * The use of the Apache License does not indicate that this project is
 * affiliated with the Apache Software Foundation.
 */
package org.mentalsmash.tazio.transactions.model.impl;

import java.io.Serializable;
import java.util.Iterator;

import org.mentalsmash.tazio.transactions.control.TazioTransaction;
import org.mentalsmash.tazio.transactions.model.identifiers.TID;
import org.mentalsmash.tazio.transactions.user.TransactionStatus;
import org.mentalsmash.tazio.transactions.user.UserTransactionManager;

import com.google.common.base.Preconditions;

/**
 * @author Andrea Reale
 * @version 0.0.1
 * 
 */
public class TransactionalIterator implements Iterator<Serializable> {

    private final UserTransactionManager tm;
    private final TID owningTransaction;
    private final Iterator<Serializable> wrappedIt;

    public TransactionalIterator(UserTransactionManager tm, TID owner,
	    Iterator<Serializable> toWrap) {
	Preconditions.checkNotNull(tm);
	Preconditions.checkNotNull(owner);
	Preconditions.checkNotNull(toWrap);

	this.tm = tm;
	this.owningTransaction = owner;
	this.wrappedIt = toWrap;
    }

    /*
     * (non-Javadoc)
     * 
     * @see java.util.Iterator#hasNext()
     */
    @Override
    public boolean hasNext() {
	Preconditions.checkState(isValid(),
		"the iterator of a TransactionalSet "
			+ "has to be used in the context of an user started "
			+ "transaction");

	return wrappedIt.hasNext();
    }

    /*
     * (non-Javadoc)
     * 
     * @see java.util.Iterator#next()
     */
    @Override
    public Serializable next() {
	Preconditions.checkState(isValid(),
		"the iterator of a TransactionalSet "
			+ "has to be used in the context of an user started "
			+ "transaction");

	return wrappedIt.next();
    }

    /**
     * @throws UnsupportedOperationException
     *             always
     */
    @Override
    public void remove() {
	throw new UnsupportedOperationException();
    }

    /**
     * A Transactional iterator is valid only if the thread using it is
     * associated to a running transaction, and that transaction is the owner of
     * the iterator
     * 
     * @return true if the TransactionalIterator is valid
     */
    private boolean isValid() {
	final TazioTransaction current = (TazioTransaction) tm.getTransaction();
	if (!current.getStatus().equals(TransactionStatus.RUNNING)) {
	    return false;
	} else {
	    return this.owningTransaction.equals(current.getTransactionId());
	}
    }

}
